Cylindrical Fresnel lenses have been used in combination with tungsten filament incandescent lamps to provide luminaires. Such luminaires have been used extensively for airway obstruction lights and beacons. When the luminaires are designed to emit light continuously, they are referred to as airway obstruction lights, and when they are designed to provide a flashing light, they are referred to as airway obstruction beacons. Classically, lamps having a horseshoe-shaped filament have been employed for such applications to provide a light source which resides substantially in a plane normal to the axis of the lens and near its center. While such luminaires have performed satisfactorily, they have not been energy efficient, and when used as beacons they have been found sufficient only when a pair of lamps and lens sections are employed. In the case of beacons, the requirement of using two lamps and lens sections increases the vertical cross section of the beacon. The lamps employed in lights and beacons also have relatively short lives, which is particularly undesirable since the luminaires are frequently not readily accessible.
Cylindrical Fresnel lenses in combination with strobe lamps have been used in some applications. However, when these strobe lamps are used the emitted light creates a time dependent pattern of short, intense bursts of light. This pattern is substantially different from either the light pattern generated by airway obstruction lights, which to provide a time independent pattern of light, or airway obstruction beacons, which provide a pattern of flashes where the duration of the "on" time is substantial.
While strobes are considered to be very effective as obstruction warning beacons from the perspective of aircraft pilots, residents in the vicinity may consider their time dependent light pattern a nuisance at night and prefer the use of red incandescent beacons. For this reason, it has become a common practice to modify nighttime strobe flashes to somewhat resemble flashes from incandescent beacons, including changing the color of the emitted light to red.
It is possible to emulate the flash pattern of an incandescent lamp beacon with an airway obstruction beacon employing a strobe lamp; however, these strobe-lit airway obstruction beacons require relatively complex circuitry to provide a perceived beam which emulates the time dependent light pattern where the duration of the "on" time of the flashes is substantial, let alone to provide a beacon which emulates a continuous light source. This circuitry increases the cost of the beacons and may foreshorten the life of the strobe lamp.
A study on the use of halogen lamps to replace the conventional tungsten filament lamps in airway obstruction beacons was reported in 1974 to the FAA by NBS (National Bureau of Standards), now NIST. In this report, various tungsten and halogen lamps were tested in combination with a standard beacon 300 mm cylindrical Fresnel lens, and it was concluded that the halogen lamps did not offer significant advantages over tungsten filament lamps. It was noted that a halogen lamp having a smaller filament provided a greater emitted light intensity, but such lamps had a prohibitively short life.